text: //===-- llvm/Value.h - Definition of the Value class ------------*- C++ -*-===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This file declares the Value class. 
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_VALUE_H
  #define LLVM_VALUE_H
  
  #include "llvm/Use.h"
  #include "llvm/Support/Casting.h"
  
  namespace llvm {
  
  class Constant;
  class Argument;
  class Instruction;
  class BasicBlock;
  class GlobalValue;
  class Function;
  class GlobalVariable;
  class GlobalAlias;
  class InlineAsm;
  class ValueSymbolTable;
  template<typename ValueTy> class StringMapEntry;
  typedef StringMapEntry<Value*> ValueName;
  class raw_ostream;
  class AssemblyAnnotationWriter;
  class ValueHandleBase;
  class LLVMContext;
  class Twine;
  class MDNode;
  class Type;
  class StringRef;
  
  //===----------------------------------------------------------------------===//
  //                                 Value Class
  //===----------------------------------------------------------------------===//
  
  /// This is a very important LLVM class. It is the base class of all values 
  /// computed by a program that may be used as operands to other values. Value is
  /// the super class of other important classes such as Instruction and Function.
  /// All Values have a Type. Type is not a subclass of Value. Some values can
  /// have a name and they belong to some Module.  Setting the name on the Value
  /// automatically updates the module's symbol table.
  ///
  /// Every value has a "use list" that keeps track of which other Values are
  /// using this Value.  A Value can also have an arbitrary number of ValueHandle
  /// objects that watch it and listen to RAUW and Destroy events.  See
  /// llvm/Support/ValueHandle.h for details.
  ///
  /// @brief LLVM Value Representation
  class Value {
    const unsigned char SubclassID;   // Subclass identifier (for isa/dyn_cast)
    unsigned char HasValueHandle : 1; // Has a ValueHandle pointing to this?
  protected:
    /// SubclassOptionalData - This member is similar to SubclassData, however it
    /// is for holding information which may be used to aid optimization, but
    /// which may be cleared to zero without affecting conservative
    /// interpretation.
    unsigned char SubclassOptionalData : 7;
  
  private:
    /// SubclassData - This member is defined by this class, but is not used for
    /// anything.  Subclasses can use it to hold whatever state they find useful.
    /// This field is initialized to zero by the ctor.
    unsigned short SubclassData;
  
    Type *VTy;
    Use *UseList;
  
    friend class ValueSymbolTable; // Allow ValueSymbolTable to directly mod Name.
    friend class ValueHandleBase;
    ValueName *Name;
  
    void operator=(const Value &);     // Do not implement
    Value(const Value &);              // Do not implement
  
  protected:
    /// printCustom - Value subclasses can override this to implement custom
    /// printing behavior.
    virtual void printCustom(raw_ostream &O) const;
  
    Value(Type *Ty, unsigned scid);
  public:
    virtual ~Value();
  
    /// dump - Support for debugging, callable in GDB: V->dump()
    //
    void dump() const;
  
    /// print - Implement operator<< on Value.
    ///
    void print(raw_ostream &O, AssemblyAnnotationWriter *AAW = 0) const;
  
    /// All values are typed, get the type of this value.
    ///
    Type *getType() const { return VTy; }
  
    /// All values hold a context through their type.
    LLVMContext &getContext() const;
  
    // All values can potentially be named.
    bool hasName() const { return Name != 0 && SubclassID != MDStringVal; }
    ValueName *getValueName() const { return Name; }
    void setValueName(ValueName *VN) { Name = VN; }
    
    /// getName() - Return a constant reference to the value's name. This is cheap
    /// and guaranteed to return the same reference as long as the value is not
    /// modified.
    StringRef getName() const;
  
    /// setName() - Change the name of the value, choosing a new unique name if
    /// the provided name is taken.
    ///
    /// \arg Name - The new name; or "" if the value's name should be removed.
    void setName(const Twine &Name);
  
    
    /// takeName - transfer the name from V to this value, setting V's name to
    /// empty.  It is an error to call V->takeName(V). 
    void takeName(Value *V);
  
    /// replaceAllUsesWith - Go through the uses list for this definition and make
    /// each use point to "V" instead of "this".  After this completes, 'this's
    /// use list is guaranteed to be empty.
    ///
    void replaceAllUsesWith(Value *V);
  
    //----------------------------------------------------------------------
    // Methods for handling the chain of uses of this Value.
    //
    typedef value_use_iterator<User>       use_iterator;
    typedef value_use_iterator<const User> const_use_iterator;
  
    bool               use_empty() const { return UseList == 0; }
    use_iterator       use_begin()       { return use_iterator(UseList); }
    const_use_iterator use_begin() const { return const_use_iterator(UseList); }
    use_iterator       use_end()         { return use_iterator(0);   }
    const_use_iterator use_end()   const { return const_use_iterator(0);   }
    User              *use_back()        { return *use_begin(); }
    const User        *use_back()  const { return *use_begin(); }
  
    /// hasOneUse - Return true if there is exactly one user of this value.  This
    /// is specialized because it is a common request and does not require
    /// traversing the whole use list.
    ///
    bool hasOneUse() const {
      const_use_iterator I = use_begin(), E = use_end();
      if (I == E) return false;
      return ++I == E;
    }
  
    /// hasNUses - Return true if this Value has exactly N users.
    ///
    bool hasNUses(unsigned N) const;
  
    /// hasNUsesOrMore - Return true if this value has N users or more.  This is
    /// logically equivalent to getNumUses() >= N.
    ///
    bool hasNUsesOrMore(unsigned N) const;
  
    bool isUsedInBasicBlock(const BasicBlock *BB) const;
  
    /// getNumUses - This method computes the number of uses of this Value.  This
    /// is a linear time operation.  Use hasOneUse, hasNUses, or hasNUsesOrMore
    /// to check for specific values.
    unsigned getNumUses() const;
  
    /// addUse - This method should only be used by the Use class.
    ///
    void addUse(Use &U) { U.addToList(&UseList); }
  
    /// An enumeration for keeping track of the concrete subclass of Value that
    /// is actually instantiated. Values of this enumeration are kept in the 
    /// Value classes SubclassID field. They are used for concrete type
    /// identification.
    enum ValueTy {
      ArgumentVal,              // This is an instance of Argument
      BasicBlockVal,            // This is an instance of BasicBlock
      FunctionVal,              // This is an instance of Function
      GlobalAliasVal,           // This is an instance of GlobalAlias
      GlobalVariableVal,        // This is an instance of GlobalVariable
      UndefValueVal,            // This is an instance of UndefValue
      BlockAddressVal,          // This is an instance of BlockAddress
      ConstantExprVal,          // This is an instance of ConstantExpr
      ConstantAggregateZeroVal, // This is an instance of ConstantAggregateZero
      ConstantDataArrayVal,     // This is an instance of ConstantDataArray
      ConstantDataVectorVal,    // This is an instance of ConstantDataVector
      ConstantIntVal,           // This is an instance of ConstantInt
      ConstantFPVal,            // This is an instance of ConstantFP
      ConstantArrayVal,         // This is an instance of ConstantArray
      ConstantStructVal,        // This is an instance of ConstantStruct
      ConstantVectorVal,        // This is an instance of ConstantVector
      ConstantPointerNullVal,   // This is an instance of ConstantPointerNull
      MDNodeVal,                // This is an instance of MDNode
      MDStringVal,              // This is an instance of MDString
      InlineAsmVal,             // This is an instance of InlineAsm
      PseudoSourceValueVal,     // This is an instance of PseudoSourceValue
      FixedStackPseudoSourceValueVal, // This is an instance of 
                                      // FixedStackPseudoSourceValue
      InstructionVal,           // This is an instance of Instruction
      // Enum values starting at InstructionVal are used for Instructions;
      // don't add new values here!
  
      // Markers:
      ConstantFirstVal = FunctionVal,
      ConstantLastVal  = ConstantPointerNullVal
    };
  
    /// getValueID - Return an ID for the concrete type of this object.  This is
    /// used to implement the classof checks.  This should not be used for any
    /// other purpose, as the values may change as LLVM evolves.  Also, note that
    /// for instructions, the Instruction's opcode is added to InstructionVal. So
    /// this means three things:
    /// # there is no value with code InstructionVal (no opcode==0).
    /// # there are more possible values for the value type than in ValueTy enum.
    /// # the InstructionVal enumerator must be the highest valued enumerator in
    ///   the ValueTy enum.
    unsigned getValueID() const {
      return SubclassID;
    }
  
    /// getRawSubclassOptionalData - Return the raw optional flags value
    /// contained in this value. This should only be used when testing two
    /// Values for equivalence.
    unsigned getRawSubclassOptionalData() const {
      return SubclassOptionalData;
    }
  
    /// clearSubclassOptionalData - Clear the optional flags contained in
    /// this value.
    void clearSubclassOptionalData() {
      SubclassOptionalData = 0;
    }
  
    /// hasSameSubclassOptionalData - Test whether the optional flags contained
    /// in this value are equal to the optional flags in the given value.
    bool hasSameSubclassOptionalData(const Value *V) const {
      return SubclassOptionalData == V->SubclassOptionalData;
    }
  
    /// intersectOptionalDataWith - Clear any optional flags in this value
    /// that are not also set in the given value.
    void intersectOptionalDataWith(const Value *V) {
      SubclassOptionalData &= V->SubclassOptionalData;
    }
  
    /// hasValueHandle - Return true if there is a value handle associated with
    /// this value.
    bool hasValueHandle() const { return HasValueHandle; }
    
    // Methods for support type inquiry through isa, cast, and dyn_cast:
    static inline bool classof(const Value *) {
      return true; // Values are always values.
    }
  
    /// stripPointerCasts - This method strips off any unneeded pointer casts and
    /// all-zero GEPs from the specified value, returning the original uncasted
    /// value. If this is called on a non-pointer value, it returns 'this'.
    Value *stripPointerCasts();
    const Value *stripPointerCasts() const {
      return const_cast<Value*>(this)->stripPointerCasts();
    }
  
    /// stripInBoundsConstantOffsets - This method strips off unneeded pointer casts and
    /// all-constant GEPs from the specified value, returning the original
    /// pointer value. If this is called on a non-pointer value, it returns
    /// 'this'.
    Value *stripInBoundsConstantOffsets();
    const Value *stripInBoundsConstantOffsets() const {
      return const_cast<Value*>(this)->stripInBoundsConstantOffsets();
    }
  
    /// stripInBoundsOffsets - This method strips off unneeded pointer casts and
    /// any in-bounds Offsets from the specified value, returning the original
    /// pointer value. If this is called on a non-pointer value, it returns
    /// 'this'.
    Value *stripInBoundsOffsets();
    const Value *stripInBoundsOffsets() const {
      return const_cast<Value*>(this)->stripInBoundsOffsets();
    }
  
    /// isDereferenceablePointer - Test if this value is always a pointer to
    /// allocated and suitably aligned memory for a simple load or store.
    bool isDereferenceablePointer() const;
    
    /// DoPHITranslation - If this value is a PHI node with CurBB as its parent,
    /// return the value in the PHI node corresponding to PredBB.  If not, return
    /// ourself.  This is useful if you want to know the value something has in a
    /// predecessor block.
    Value *DoPHITranslation(const BasicBlock *CurBB, const BasicBlock *PredBB);
  
    const Value *DoPHITranslation(const BasicBlock *CurBB,
                                  const BasicBlock *PredBB) const{
      return const_cast<Value*>(this)->DoPHITranslation(CurBB, PredBB);
    }
    
    /// MaximumAlignment - This is the greatest alignment value supported by
    /// load, store, and alloca instructions, and global values.
    static const unsigned MaximumAlignment = 1u << 29;
    
    /// mutateType - Mutate the type of this Value to be of the specified type.
    /// Note that this is an extremely dangerous operation which can create
    /// completely invalid IR very easily.  It is strongly recommended that you
    /// recreate IR objects with the right types instead of mutating them in
    /// place.
    void mutateType(Type *Ty) {
      VTy = Ty;
    }
    
  protected:
    unsigned short getSubclassDataFromValue() const { return SubclassData; }
    void setValueSubclassData(unsigned short D) { SubclassData = D; }
  };
  
  inline raw_ostream &operator<<(raw_ostream &OS, const Value &V) {
    V.print(OS);
    return OS;
  }
    
  void Use::set(Value *V) {
    if (Val) removeFromList();
    Val = V;
    if (V) V->addUse(*this);
  }
  
  
  // isa - Provide some specializations of isa so that we don't have to include
  // the subtype header files to test to see if the value is a subclass...
  //
  template <> struct isa_impl<Constant, Value> {
    static inline bool doit(const Value &Val) {
      return Val.getValueID() >= Value::ConstantFirstVal &&
        Val.getValueID() <= Value::ConstantLastVal;
    }
  };
  
  template <> struct isa_impl<Argument, Value> {
    static inline bool doit (const Value &Val) {
      return Val.getValueID() == Value::ArgumentVal;
    }
  };
  
  template <> struct isa_impl<InlineAsm, Value> { 
    static inline bool doit(const Value &Val) {
      return Val.getValueID() == Value::InlineAsmVal;
    }
  };
  
  template <> struct isa_impl<Instruction, Value> { 
    static inline bool doit(const Value &Val) {
      return Val.getValueID() >= Value::InstructionVal;
    }
  };
  
  template <> struct isa_impl<BasicBlock, Value> { 
    static inline bool doit(const Value &Val) {
      return Val.getValueID() == Value::BasicBlockVal;
    }
  };
  
  template <> struct isa_impl<Function, Value> { 
    static inline bool doit(const Value &Val) {
      return Val.getValueID() == Value::FunctionVal;
    }
  };
  
  template <> struct isa_impl<GlobalVariable, Value> { 
    static inline bool doit(const Value &Val) {
      return Val.getValueID() == Value::GlobalVariableVal;
    }
  };
  
  template <> struct isa_impl<GlobalAlias, Value> { 
    static inline bool doit(const Value &Val) {
      return Val.getValueID() == Value::GlobalAliasVal;
    }
  };
  
  template <> struct isa_impl<GlobalValue, Value> { 
    static inline bool doit(const Value &Val) {
      return isa<GlobalVariable>(Val) || isa<Function>(Val) ||
        isa<GlobalAlias>(Val);
    }
  };
  
  template <> struct isa_impl<MDNode, Value> { 
    static inline bool doit(const Value &Val) {
      return Val.getValueID() == Value::MDNodeVal;
    }
  };
    
  // Value* is only 4-byte aligned.
  template<>
  class PointerLikeTypeTraits<Value*> {
    typedef Value* PT;
  public:
    static inline void *getAsVoidPointer(PT P) { return P; }
    static inline PT getFromVoidPointer(void *P) {
      return static_cast<PT>(P);
    }
    enum { NumLowBitsAvailable = 2 };
  };
  
  } // End llvm namespace
  
  #endif
  